1. Technical Field
The present invention relates to a rotary electric machine having a stator and a rotor.
2. Related Art
In related art, there is disclosed a technique for a permanent magnet rotary electric machine, in order to reduce a peak value of an induced voltage generated when a vehicle is braked or traveling downhill (see, for example, JP-B2-3370901). This permanent magnet rotary electric machine has a stator and a rotor with a plurality of permanent magnets. In the stator, a plurality of slots are formed. In these slots, three-phase stator windings, i.e., U-phase, V-phase and W phase windings are held. This rotary electric machine is configured so as to satisfy θ≈(n+0.5)×τs where n is a natural number, τs a slot pitch of the stator, and θ is an angle of a circumferential width of a stator side face of the respective permanent magnets relative to an axis of the rotor.
However, when the permanent magnet rotary electric machine disclosed in JP-B2-3370901 increases the number of slots, its back electromotive force (B-EMF) is likely to have a waveform with large harmonic distortion. For example, such a waveform is largely affected by an (Sn/Po)±first order harmonic component, where Sn is the number of slots and Po is the number of pole pairs. Thus, an additional circuit element such as a capacitor having capacitance capable of cancelling increase of the B-EMF is required to keep impact of the harmonic components on the waveform of the B-EMF low. This causes a large capacitance or a large body.
In addition, total harmonic distortion (THD) is expressed by the following formula (1):
                              T          ⁢                                          ⁢          H          ⁢                                          ⁢          D                =                                                            V                2                2                            +                              V                3                2                            +                              V                4                2                            +              …              +                              V                n                2                                                          V            1                                              (        1        )            
where V1 is an amplitude of a fundamental wave (sinusoidal wave), and V2, V3, . . . , Vn are harmonic components having frequencies equal to integral multiples of frequency of the fundamental wave (n is an integer and the highest order of the harmonic components).
The THD in the formula (1) shows that the waveform is how much distortion exists with respect to the fundamental wave. The stronger the harmonic components, the higher the THD. For example, FIG. 26 is a graph representing an amplitude variation of 5-th, 7-th, 11-th, and 13-th harmonic components relative to the fundamental wave waveform with respect to an arc ratio θa, which is an angle indicating a range in which magnetic flux radially flows from the magnet section in related art. As shown in FIG. 26, the 11-th harmonic component relative to the fundamental wave represents the maximum value at each point, and therefore, the THD is high. Further, a problem occurs in that, the more intense harmonic components are, the stronger the noise vibration (NZ) is.